1. Field of the Invention
The present invention relates to the production of a nonwoven web of fabric that has characteristics similar to woven and knitted fabrics.
2. Description of the Related Art
It has long been desirable to create a nonwoven web of fabric that looks and feels like woven cloth. However, attempts at achieving such a fabric have been unsuccessful. For example, in spunbond or meltblown processes, extruded fibers are typically laid on a web forming surface, such as a forming table or screen belt, to form a web which is then bonded utilizing calender rolls or some similar bonding device to form the nonwoven fabric. The bonding of the web results in bond points between fibers that are too visible to the naked eye up to distances of about three feet from the fabric. The visibility of these bond points can be aesthetically undesirable depending upon the type of textile article to be produced utilizing this fabric. In addition, non-uniform fiber distribution in the formation of the fabric and the distance between bond points results in a fabric with rather random porosity and with visible holes in the fabric, which limits the strength and durability of the fabric.
Other problems associated with forming nonwoven webs of fabric can occur when using heat shrinkable polymer fibers such as polyester fibers. In particular, it is well known that spunbond polyester fibers tend to shrink, particularly when spun at spinning speeds below about 3500 meters per minute (MPM), by 50% or more during any post-spun heat treating process. Polyester fibers exhibit similar heat shrinking characteristics when produced utilizing a meltblown or other fiber forming process. The reason for this is that the polyester fibers are relatively amorphous after extrusion, but achieve a higher degree of crystallinity when subjected to heat which causes shrinkage of the fibers. When heat bonding such polyester (or other similar heat shrinkable polymer) fibers together, the shrinking fibers yield a resultant nonwoven fabric that is stiff and board-like. Manufacturers typically go to great lengths to eliminate the high shrinkage of polyester during nonwoven fabric formation, employing such techniques as adjusting calender roll temperatures, utilizing complex equipment to achieve higher spinning speeds during fiber extrusion, and applying heat at varying stages to the extruded fibers.
Thus, it is desirable to obtain a nonwoven web of fabric material that has the look and feel of woven and knitted fabrics by eliminating visible bond points and reducing or controlling porosity within the bonded web without imparting undesirable stiffness to the fabric material.